Refueling systems and methods for mixed liquid and gaseous fuel

ABSTRACT

A fuel tank system, comprising: a fuel tank configured to store a liquid fuel and a pressurized gaseous fuel capable of partially dissolving in the liquid fuel; a refueling conduit coupled to the fuel tank via a tank access valve; a first high pressure refueling port coupled to the refueling conduit; a low pressure refueling port coupled to the refueling conduit via a check valve. In this way, pressurized gaseous fuel or a pre-pressurized mix of fuels may be added to the fuel tank without active control any time the fuel pressure in the fuel tank is below a maximum allowable pressure, and liquid fuel may be added to the fuel tank with active control whenever the fuel pressure and liquid fuel level in the fuel tank are below threshold levels.

BACKGROUND AND SUMMARY

Compressed natural gas (CNG) is a high octane fuel that is beneficialfor reducing engine knock, for reducing hydrocarbon emissions in coldstart events, and for reducing carbon dioxide emissions during engineoperations. However, CNG has a low energy density compared to liquidhydrocarbon fuels, such as diesel fuel or gasoline. This typicallyrequires packaging of CNG in cryogenic quality tanks (as liquifiednatural gas (LNG)) or in high pressure tanks (approximately 200-250atmospheres).

To increase the range and total fuel quantity stored in a vehicle, CNGmay be utilized in conjunction with gasoline or diesel fuel, requiringthe vehicle to switch between fuels for optimal performance. However,space constraints do not allow for the inclusion of separate fuel tanksto all vehicles. A preferable system may be one that stores liquid fueland pressurized gaseous fuel together in a single tank. In particular,CNG is able to partially dissolve in gasoline or diesel fuel when storedtogether at a relatively low pressure (˜100 atm).

Storing a mix of pressurized gaseous fuel and low pressure liquid fuelwithin a single tank presents challenges for refueling. It may bepossible to add liquid fuel to the tank first, then pressurize the tankwith pressurized gaseous fuel, or to add a pre-pressurized fuel mix.However, it may not always be practical to empty the tank completelybefore refueling, and pre-pressurized fuel mixtures may not always beavailable at refueling stations. Current refueling systems do not allowfor the addition of either pressurized gaseous fuel or low pressureliquid fuel or a pre-pressurized fuel mix to a single tank whenrefueling and/or as fuel is available at refueling stations.

The inventors herein have recognized the above problems, and developedsystems and methods to at least partially address these issues. In oneexample, a fuel tank system, comprising: a fuel tank configured to storea liquid fuel and a pressurized gaseous fuel capable of partiallydissolving in the liquid fuel; a refueling conduit coupled to the fueltank via a tank access valve; a first high pressure refueling portcoupled to the refueling conduit; a low pressure refueling port coupledto the refueling conduit via a check valve. In this way, pressurizedgaseous fuel or a pre-pressurized mix of fuels may be added to the fueltank without active control any time the fuel pressure in the fuel tankis below a maximum allowable pressure, and liquid fuel may be added tothe fuel tank with active control whenever the fuel pressure and liquidfuel level in the fuel tank are below threshold levels.

In another example, a method for refueling a vehicle fuel tank,comprising: responsive to a first condition, pumping liquid fuel from asurge tank into a fuel tank, while storing a liquid fuel and apressurized gaseous fuel only partially dissolved in the liquid fuel inthe tank. In this way, liquid fuel can be added to a fuel tank withoutrequiring the tank pressure to approach zero, allowing for moreopportunities to add liquid fuel to the fuel tank.

In yet another example, a method for refueling a vehicle fuel tank,comprising: responsive to a first condition, pumping gaseous fuel from afuel tank into a secondary vapor tank, while storing a liquid fuel and apressurized gaseous fuel only partially dissolved in the liquid fuel inthe tank. In this way, a mixed fuel tank may be relieved of a highpressure, allowing for the addition of liquid fuel without combustingadditional gaseous fuel.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 schematically depicts an example embodiment of a cylinder of aninternal combustion engine.

FIG. 2 shows a schematic depiction of an engine and fuel systemconfigured to operate on a mix of gaseous fuel and liquid fuel.

FIG. 3 shows a schematic depiction of an alternate engine and systemconfigured to operate on a mix of gaseous fuel and liquid fuel.

FIG. 4 shows an example high level flowchart for refueling the enginesystem of FIG. 2 with liquid fuel.

FIG. 5 shows and example high level flowchart for refueling the enginesystem of 3 with liquid fuel.

DETAILED DESCRIPTION

The present description relates to systems and methods for refueling avehicle or an engine system including a fuel system that operates onboth liquid fuel and gaseous fuel, the two fuels stored together in ahigh pressure fuel tank. The engine system may include a cylinderconfigured with both a port fuel injector and a direct fuel injector asshown in FIG. 1. The engine system may include a multi-cylinder enginecoupled to a fuel system with a refueling system as depicted in FIG. 2.Alternatively, the engine system may include a refueling system asdepicted in FIG. 3. FIG. 4 illustrates a method for adding liquid fuelto the engine system of FIG. 2. Additionally, FIG. 5 illustrates amethod for adding liquid fuel to the engine system of FIG. 3.

FIG. 1 depicts an example embodiment of a combustion chamber or cylinderof internal combustion engine 10. Engine 10 may be controlled at leastpartially by a control system including controller 12 and by input froma vehicle operator 130 via an input device 132. In this example, inputdevice 132 includes an accelerator pedal and a pedal position sensor 134for generating a proportional pedal position signal PP. Cylinder (i.e.combustion chamber) 14 of engine 10 may include combustion chamber walls136 with piston 138 positioned therein. Piston 138 may be coupled tocrankshaft 140 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. Crankshaft 140 may be coupledto at least one drive wheel of the passenger vehicle via a transmissionsystem. Further, a starter motor may be coupled to crankshaft 140 via aflywheel to enable a starting operation of engine 10.

Cylinder 14 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 can communicate with othercylinders of engine 10 in addition to cylinder 14. In some embodiments,one or more of the intake passages may include a boosting device such asa turbocharger or a supercharger. For example, FIG. 1 shows engine 10configured with a turbocharger including a compressor 174 arrangedbetween intake passages 142 and 144, and an exhaust turbine 176 arrangedalong exhaust passage 148. Compressor 174 may be at least partiallypowered by exhaust turbine 176 via a shaft 180 where the boosting deviceis configured as a turbocharger. However, in other examples, such aswhere engine 10 is provided with a supercharger, exhaust turbine 176 maybe optionally omitted, where compressor 174 may be powered by mechanicalinput from a motor or the engine. A throttle 162 including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 162 may be disposed downstreamof compressor 174 as shown in FIG. 1, or may alternatively be providedupstream of compressor 174.

Exhaust passage 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 14. Exhaust gas sensor 128 is showncoupled to exhaust passage 148 upstream of emission control device 178.Sensor 128 may be any suitable sensor for providing an indication ofexhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO(universal or wide-range exhaust gas oxygen), a two-state oxygen sensoror EGO (as depicted), a HEGO (heated EGO), a NOx, HC, or CO sensor.Emission control device 178 may be a three way catalyst (TWC), NOx trap,various other emission control devices, or combinations thereof.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 14 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 14. In some embodiments, eachcylinder of engine 10, including cylinder 14, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 via actuator 152.Similarly, exhaust valve 156 may be controlled by controller 12 viaactuator 154. During some conditions, controller 12 may vary the signalsprovided to actuators 152 and 154 to control the opening and closing ofthe respective intake and exhaust valves. The position of intake valve150 and exhaust valve 156 may be determined by respective valve positionsensors (not shown). The valve actuators may be of the electric valveactuation type or cam actuation type, or a combination thereof. Theintake and exhaust valve timing may be controlled concurrently or any ofa possibility of variable intake cam timing, variable exhaust camtiming, dual independent variable cam timing or fixed cam timing may beused. Each cam actuation system may include one or more cams and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems that may be operated by controller 12 to vary valve operation.For example, cylinder 14 may alternatively include an intake valvecontrolled via electric valve actuation and an exhaust valve controlledvia cam actuation including CPS and/or VCT. In other embodiments, theintake and exhaust valves may be controlled by a common valve actuatoror actuation system, or a variable valve timing actuator or actuationsystem.

Cylinder 14 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen for example when higher octane fuels or fuelswith higher latent enthalpy of vaporization are used. The compressionratio may also be increased if direct injection is used due to itseffect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 14 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 14 is shown including two fuel injectors 166 and 170.Fuel injector 166 is shown coupled directly to cylinder 14 for injectingfuel directly therein in proportion to the pulse width of signal FPW-1received from controller 12 via electronic driver 168. In this manner,fuel injector 166 provides what is known as direct injection (hereafterreferred to as “DI”) of fuel into combustion cylinder 14. While FIG. 1shows injector 166 as a side injector, it may also be located overheadof the piston, such as near the position of spark plug 192. Such aposition may improve mixing and combustion when operating the enginewith an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing. Fuel may be delivered tofuel injector 166 from fuel system 172 including a fuel tank, fuelpumps, a fuel rail, and driver 168. Alternatively, fuel may be deliveredby a single stage fuel pump at lower pressure, in which case the timingof the direct fuel injection may be more limited during the compressionstroke than if a high pressure fuel system is used. Further, while notshown, the fuel tank may have a pressure transducer providing a signalto controller 12.

Fuel injector 170 is shown arranged in intake passage 146, rather thanin cylinder 14, in a configuration that provides what is known as portinjection of fuel (hereafter referred to as “PFI”) into the intake portupstream of cylinder 14. Fuel injector 170 may inject fuel in proportionto the pulse width of signal FPW-2 received from controller 12 viaelectronic driver 171. Fuel may be delivered to fuel injector 170 byfuel system 172.

Fuel may be delivered by both injectors to the cylinder during a singlecycle of the cylinder. For example, each injector may deliver a portionof a total fuel injection that is combusted in cylinder 14. Further, thedistribution and/or relative amount of fuel delivered from each injectormay vary with operating conditions such as described herein below. Therelative distribution of the total injected fuel among injectors 166 and170 may be referred to as a first injection ratio. For example,injecting a larger amount of the fuel for a combustion event via (port)injector 170 may be an example of a higher first ratio of port to directinjection, while injecting a larger amount of the fuel for a combustionevent via (direct) injector 166 may be a lower first ratio of port todirect injection. Note that these are merely examples of differentinjection ratios, and various other injection ratios may be used.Additionally, it should be appreciated that port injected fuel may bedelivered during an open intake valve event, closed intake valve event(e.g., substantially before an intake stroke, such as during an exhauststroke), as well as during both open and closed intake valve operation.Similarly, directly injected fuel may be delivered during an intakestroke, as well as partly during a previous exhaust stroke, during theintake stroke, and partly during the compression stroke, for example.Further, the direct injected fuel may be delivered as a single injectionor multiple injections. These may include multiple injections during thecompression stroke, multiple injections during the intake stroke or acombination of some direct injections during the compression stroke andsome during the intake stroke. When multiple direct injections areperformed, the relative distribution of the total directed injected fuelbetween an intake stroke (direct) injection and a compression stroke(direct) injection may be referred to as a second injection ratio. Forexample, injecting a larger amount of the direct injected fuel for acombustion event during an intake stroke may be an example of a highersecond ratio of intake stroke direct injection, while injecting a largeramount of the fuel for a combustion event during a compression strokemay be an example of a lower second ratio of intake stroke directinjection. Note that these are merely examples of different injectionratios, and various other injection ratios may be used.

As such, even for a single combustion event, injected fuel may beinjected at different timings from a port and direct injector.Furthermore, for a single combustion event, multiple injections of thedelivered fuel may be performed per cycle. The multiple injections maybe performed during the compression stroke, intake stroke, or anyappropriate combination thereof.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine. As such each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc.

Fuel injectors 166 and 170 may have different characteristics. Theseinclude differences in size, for example, one injector may have a largerinjection hole than the other. Other differences include, but are notlimited to, different spray angles, different operating temperatures,different targeting, different injection timing, different spraycharacteristics, different locations etc. Moreover, depending on thedistribution ratio of injected fuel among injectors 170 and 166,different effects may be achieved.

Fuel system 172 may include one fuel tank or multiple fuel tanks. Inembodiments where fuel system 172 includes multiple fuel tanks, the fueltanks may hold fuel with the same fuel qualities or may hold fuel withdifferent fuel qualities, such as different fuel compositions. Thesedifferences may include different alcohol content, different octane,different heat of vaporizations, different fuel blends, and/orcombinations thereof etc. In one example, fuels with different alcoholcontents could include gasoline, ethanol, methanol, or alcohol blendssuch as E85 (which is approximately 85% ethanol and 15% gasoline) or M85(which is approximately 85% methanol and 15% gasoline). Other alcoholcontaining fuels could be a mixture of alcohol and water, a mixture ofalcohol, water and gasoline etc. In some examples, fuel system 172 mayinclude a fuel tank that holds a liquid fuel, such as gasoline, and alsoholds a gaseous fuel, such as CNG. Fuel injectors 166 and 170 may beconfigured to inject fuel from the same fuel tank, from different fueltanks, from a plurality of the same fuel tanks, or from an overlappingset of fuel tanks. While FIG. 1 depicts fuel injector 166 as a directfuel injector and fuel injector 170 as a port fuel injector, in otherembodiments both injectors 166 and 170 may be configured as port fuelinjectors or may both be configured as direct fuel injectors.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 106, input/output ports 108, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 110 in this particular example, random access memory 112,keep alive memory 114, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal (PIP) from Hall effect sensor 120 (or other type)coupled to crankshaft 140; throttle position (TP) from a throttleposition sensor; and absolute manifold pressure signal (MAP) from sensor124. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold.

Storage medium read-only memory 110 can be programmed with computerreadable data representing instructions executable by processor 106 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed. Example routines that maybe performed by the controller are described herein and with regards toFIGS. 3 and 4.

FIG. 2 shows a schematic diagram of a multi-cylinder engine inaccordance with the present disclosure. As depicted in FIG. 1, internalcombustion engine 10 includes cylinders 14 coupled to intake passage 144and exhaust passage 148. Intake passage 144 may include throttle 162.Exhaust passage 148 may include emissions control device 178.

Cylinders 14 may be configured as part of cylinder head 201. In FIG. 2,cylinder head 201 is shown with 4 cylinders in an inline configuration.In some examples, cylinder head 201 may have more or fewer cylinders,for example six cylinders. In some examples, the cylinders may bearranged in a V configuration or other suitable configuration.

Cylinder head 201 is shown coupled to fuel system 172. Cylinder 14 isshown coupled to fuel injectors 166 and 170. Although only one cylinderis shown coupled to fuel injectors, it is to be understood that allcylinders 14 included in cylinder head 201 may also be coupled to one ormore fuel injectors. In this example embodiment, fuel injector 166 isdepicted as a direct fuel injector and fuel injector 170 is depicted asa port fuel injector. Each fuel injector may be configured to deliver aspecific quantity of fuel at a specific time point in the engine cyclein response to commands from controller 12. One or both fuel injectorsmay be utilized to deliver combustible fuel to cylinder 14 during eachcombustion cycle. The timing and quantity of fuel injection may becontrolled as a function of engine operating conditions.

Fuel system 172 includes fuel tank 200. Fuel tank 200 may include aliquid fuel, such as gasoline, diesel fuel, or a gasoline-alcohol blend(e.g. E10, E85, M15, or M85), and may also include a gaseous fuel, suchas CNG. Fuel tank 200 may be configured to store liquid fuel and gaseousfuel together at a relatively low pressure compared to conventional CNGstorage (e.g. 200-250 atmospheres). For example, the gaseous fuel may beadded to a pressure of 100 atmospheres. In this way, a portion of thegaseous fuel may be dissolved in the liquid fuel. At 100 atmospheres,CNG may dissolve in gasoline to the point where 40% of the liquid fuelcomponent in fuel tank 200 is CNG. Fuel tank 200 may include pressuresensor 211, temperature sensor 212, and liquid level sensor 215.

Fuel injector 166 may be coupled to fuel tank 200 in a configurationwhere liquid fuel stored in fuel tank 200 is delivered to fuel injector166. Fuel injector 166 is shown coupled to fuel rail 205. Fuel rail 205may be coupled to fuel line 220. Fuel rail 205 may include one or moresensors, such as pressure or temperature sensors. Fuel line 220 iscoupled to fuel tank 200. Fuel line 220 may be coupled to a lowerportion of fuel tank 200 in order draw liquid fuel from fuel tank 200.Fuel line may be coupled to fuel pump 210. In some cases, fuel pump 210may be omitted from fuel system 172. In such embodiments, the pressureof gaseous fuel stored in fuel tank 200 may be used to drive liquid fuelfrom fuel tank 200 to fuel rail 205 via fuel line 220. In embodimentswhere fuel pump 210 is omitted, a liquid fuel valve may be coupled tofuel line 220 to control liquid fuel flow through fuel line 220.

Fuel injector 170 may be coupled to fuel tank 200 in a configurationwhere gaseous fuel stored in fuel tank 200 is delivered to fuel injector170. Fuel injector 170 is shown coupled to fuel rail 206. Fuel rail 206may be coupled to fuel line 221. Fuel rail 206 may include one or moresensors, such as pressure or temperature sensors. Fuel line 221 iscoupled to fuel tank 200. Fuel line 221 may be coupled to an upperportion of fuel tank 200 in order to draw gaseous fuel from fuel tank200. Fuel line 221 may be coupled to one or more fuel pumps. Fuel line221 may include a line valve, a pressure relief valve, a coalescingfilter, and/or a pressure regulator. Fuel rail 206 may be configured tobe a higher pressure fuel rail, and fuel rail 205 may be configured tobe a lower pressure fuel rail. Fuel rail 205 may be configured to holdliquid fuel at a lower pressure than fuel tank 200. In such embodiments,some gaseous fuel may volatize from the liquid fuel/gaseous fuelemulsion. A pressure relief valve and/or scavenging line may be coupledto fuel rail 205 such that only liquid fuel is injected through fuelinjector 166, and such that the gaseous fuel is removed and/or recycledfrom fuel system 172. In some embodiments, both fuel injectors 166 and170 may be port fuel injectors, or both may be direct fuel injectors.Alternatively, liquid fuel injector 166 may be configured as a port fuelinjector and gaseous fuel injector 170 may be a direct fuel injector.

Fuel system 172 is shown coupled to refueling system 250. Refuelingsystem 250 may be coupled to fuel tank 200 via tank access valve 218.Tank access valve 218 may be coupled to refueling conduit 260. Refuelingconduit 260 may include high pressure refueling port 255. High pressurerefueling port 255 may be configured to receive a pressurized gaseousfuel pump nozzle, or a fuel pump nozzle configured to deliver apre-pressured mixture of liquid fuel and gaseous fuel. In some cases, asecond high pressure refueling port may be included to allowcompatibility with more than one type of high pressure fuel pump nozzle.

Access to high pressure refueling port 255 may be regulated by refuelinglock 257. In some embodiments, refueling lock 257 may be a fuel caplocking mechanism. The fuel cap locking mechanism may be configured toautomatically lock a fuel cap in a closed position so that the fuel capcannot be opened. For example, the fuel cap may remain locked viarefueling lock 257 while pressure in the fuel tank is greater than athreshold. A fuel cap locking mechanism may be a latch or clutch, which,when engaged, prevents the removal of the fuel cap. The latch or clutchmay be electrically locked, for example, by a solenoid, or may bemechanically locked, for example, by a pressure diaphragm.

In some embodiments, refueling lock 257 may be a filler pipe valvelocated at a mouth of refueling conduit 260. In such embodiments,refueling lock 257 may prevent the insertion of a refueling pump intorefueling conduit 260. The filler pipe valve may be electrically locked,for example by a solenoid, or mechanically locked, for example by apressure diaphragm.

In some embodiments, refueling lock 257 may be a refueling door lock,such as a latch or a clutch which locks a refueling door located in abody panel of the vehicle. The refueling door lock may be electricallylocked, for example by a solenoid, or mechanically locked, for exampleby a pressure diaphragm.

In embodiments where refueling lock 257 is locked using an electricalmechanism, refueling lock 257 may be unlocked by commands fromcontroller 12, for example, when a fuel tank pressure decreases below apressure threshold. In embodiments where refueling lock 257 is lockedusing a mechanical mechanism, refueling lock 257 may be unlocked via apressure gradient, for example, when a fuel tank pressure decreasesbelow a threshold.

Refueling conduit 260 may be coupled to low pressure refueling conduit280. Low pressure refueling conduit 280 may be coupled to surge tank270. Surge tank 270 may include a low pressure refueling port 265 and aliquid sensor 275. Low pressure refueling conduit 280 may include fuelpump 285 and check valve 290. Fuel pump 285 may only operate when fueltank pressure is below a threshold, and may only operate when there isliquid fuel in surge tank 270, as sensed by liquid sensor 275. In thisway, fuel pump 285 may not pump an air/fuel mixture into fuel tank 200.Further, when fuel tank pressure reaches a threshold, fuel pump 285 maybe shut off by controller 12, causing liquid fuel to accumulate in surgetank 270. This may cause a low pressure liquid fuel dispenser nozzleengaged with low pressure refueling port 265 to turn itself off. Accessto refueling port 265 may be regulated by refueling lock 267. Refuelinglock 267 may be comprise one of the examples described for refuelinglock 257. Refueling locks 257 and 267 may comprise different mechanisms,and may be responsive to different tank pressure thresholds. An examplerefueling routine for the system depicted in FIG. 2 is described hereinand with regards to FIG. 4.

FIG. 3 shows an alternative schematic diagram of a multi-cylinder enginein accordance with the present disclosure. As described herein anddepicted in FIG. 2, multicylinder engine 10 includes cylinders 14coupled to intake passage 144 and exhaust passage 148, and furthercoupled to fuel system 172. Fuel system 172 is configured to store amixture of liquid fuel and pressurized gaseous fuel in fuel tank 200,and further to deliver liquid fuel to direct fuel injector 166 and todeliver gaseous fuel to port fuel injector 170. As described herein andwith regards to FIG. 2, some embodiments may include fuel injectors 166and 170 in different configurations than the configuration depicted inFIG. 3. In the embodiment shown in FIG. 3, fuel system 172 is coupled torefueling system 350.

In the embodiment depicted in FIG. 3, refueling system 350 is coupled tofuel tank 200 via tank access valve 218. Tank access valve 218 may becoupled to refueling conduit 360. Refueling conduit 360 may include highpressure refueling port 355. High pressure refueling port 355 may beconfigured to receive a pressurized gaseous fuel pump nozzle, or a fuelpump nozzle configured to deliver a pre-pressured mixture of liquid fueland gaseous fuel. In some embodiments, a second high pressure refuelingport may be included to allow compatibility with more than one type ofhigh pressure fuel pump nozzles. In some embodiments, access to highpressure refueling port 355 may be regulated by refueling lock 357.

Refueling conduit 360 may be coupled to low pressure refueling conduit370. Low pressure refueling conduit 370 may include low pressurerefueling port 365 and check valve 375. Access to low pressure refuelingport 365 may be regulated by refueling lock 367. Optionally, a secondarytank 390 may be coupled to fuel tank 200 via gaseous fuel line 380. Pump385 may be coupled to gaseous fuel line 380. Pump 385 may be activatedto pump gaseous fuel out of fuel tank 200 and into secondary tank 390.In the absence of secondary tank 390, liquid fuel may only be added tofuel tank 200 when pressure in fuel tank 200 is at or near zero. If apositive pressure exists in fuel tank 200, check valve 375 will forceliquid fuel entering low pressure refueling port 365 to quickly fill lowpressure refueling conduit 370, causing a low pressure liquid fueldispenser nozzle engaged with low pressure refueling port 365 to turnitself off

However, when secondary tank 390 is included in refueling system 350,fuel tank 200 may be actively depressurized to allow refueling with lowpressure liquid fuel. Pump 385 may be activated to pump gaseous fuel orfuel vapor into secondary tank 390. Upon the tank pressure in fuel tank200 decreasing below a threshold, refueling with low pressure liquidfuel may be allowed, for example by unlocking refueling lock 367. Anexample refueling routine for the system depicted in FIG. 3 is describedherein and with respect to FIG. 5.

FIG. 4 depicts an example routine 400 for a high-level method forrefueling a mixed liquid hydrocarbon/gaseous fuel system. In particular,routine 400 describes a method for liquid fuel refueling in a mixed fuelsystem. Routine 400 will be described herein with reference to thecomponents and systems depicted in FIGS. 1 and 2, though the method maybe applied to other systems without departing from the scope of thisdisclosure. Routine 400 may be carried out by controller 12, and may bestored as executable instructions in non-transitory memory.

Routine 400 may begin at 410 by determining whether liquid refueling isdesired. Determining whether liquid refueling is desired may includedirect or indirect liquid refueling requests from the vehicle operator.Direct refueling requests may include explicit operator requests madethrough an interface or detection of an operator opening a refuelingdoor. Indirect liquid refueling requests may include the detection of aproximity to a refueling station. Proximity to a refueling station maybe determined through GPS or other location data, or based on directcommunication between the vehicle and refueling station. If no direct orindirect liquid refueling request is detected, method 400 may proceed to415. At 415, method 400 may include maintaining liquid refueling lock267 closed. Method 400 may then end.

If a direct or indirect liquid refueling request is detected at 410,method 400 may proceed to 420. At 420, method 400 may includedetermining whether conditions suitable for liquid refueling are met.Liquid refueling conditions may include a fuel tank pressure being belowa threshold and/or a fuel tank liquid level being below a threshold.Fuel tank pressure may be measured by a pressure sensor, such aspressure sensor 211. Fuel tank liquid level may be measured by a liquidlevel sensor, such as liquid level sensor 215. Other conditions, such asfuel tank temperature, ambient temperature, atmospheric pressure, etc.may be gauged to determine whether liquid fuel can be added to fuel tank200. If liquid refueling conditions are not met (e.g. fuel tank pressureis above a threshold) method 400 may proceed to 415. At 415, method 400may include maintaining liquid refueling lock 267 closed. Method 400 maythen end.

If liquid refueling conditions are met at 420, method 400 may proceed to430. At 430, method 400 may include opening the liquid refueling lock.This may allow the vehicle operator or refueling station attendant toopen a refueling door, remove a gas cap, and/or engage a liquidrefueling nozzle with low pressure refueling port 265.

Continuing at 440, method 400 may include determining whether there isliquid fuel in the surge tank. For example, the presence of liquid fuelin surge tank 270 may be determined through a liquid sensor, such asliquid sensor 275. If there is no liquid fuel in the surge tank, method400 may proceed to 445. At 445, method 400 may include deactivating therefueling pump, such as fuel pump 285 as shown in FIG. 2. If therefueling pump is not currently active, the fuel pump may be maintainedin an inactive state. Method 400 may then end.

If there is liquid fuel in the surge tank, as determined at 440, method400 may proceed to 450. At 450, method 400 may include determiningwhether pressure in the main fuel tank is greater than a threshold. Fueltank pressure may be determined via fuel tank pressure sensor 211. Ifthe fuel tank pressure is greater than the threshold, method 400 mayproceed to 445. At 445, method 400 may include deactivating therefueling pump, such as fuel pump 285 as shown in FIG. 2. If therefueling pump is not currently active, the fuel pump may be maintainedin an inactive state. Method 400 may then end.

If fuel tank pressure is less than a threshold, as determined at 450,method 400 may proceed to 460. At 460, method 400 may includedetermining whether the liquid level in the main fuel tank is above athreshold. Fuel tank liquid level may be determined via fuel tank liquidlevel sensor 215. If the fuel tank liquid level is greater than thethreshold, method 400 may proceed to 445. At 445, method 400 may includedeactivating the refueling pump, such as fuel pump 285 as shown in FIG.2. If the refueling pump is not currently active, the fuel pump may bemaintained in an inactive state. Method 400 may then end.

If the fuel tank liquid level is less than a threshold, as determined at460, method 400 may proceed to 470. At 470, method 400 may includeactivating the refueling pump, and pumping liquid fuel from the surgetank to the main fuel tank. Pumping liquid fuel from the surge tank tothe main fuel tank may continue until there is no longer liquid fuel inthe surge tank, until the fuel tank pressure increases above athreshold, and/or until the fuel tank liquid level increases above athreshold. Method 400 may iterate from 440 to 470 in order to accomplishfuel tank filling. In some embodiments controller 12 may determine anamount of fuel which may be added to fuel tank 200 without increasingabove a pressure threshold or a liquid level threshold, and continueoperation of fuel pump 285 until the predetermined amount of fuel hasbeen added to the fuel tank, as long as liquid fuel remains in the surgetank. Method 400 may then end.

The systems described herein and depicted in FIGS. 1 and 2 and themethods described herein and depicted in FIG. 4 may enable one or moremethods. In one example, a method for refueling a vehicle fuel tank,comprising: responsive to a first condition, pumping liquid fuel from asurge tank into a fuel tank, while storing a hydrocarbon liquid fuel anda pressurized gaseous fuel only partially dissolved in the hydrocarbonliquid fuel in the tank. The first condition may include the detectionof a liquid refueling request; a fuel tank pressure that is less than afirst threshold; a fuel tank liquid level that is less than a secondthreshold; and a surge tank liquid level that is greater than a thirdthreshold. The method may further comprise: responsive to a secondcondition, ceasing the pumping of liquid fuel from the surge tank intothe fuel tank. The second condition may include a surge tank liquidlevel that is less than the third threshold. The technical result ofimplementing this method is that liquid fuel may be added whenever fueltank pressure and fuel tank liquid level are below thresholds.Implementing this method may allow liquid fuel to be added to the fueltank without an air/fuel mixture being added to the fuel tank, therebyavoiding the creation of a combustible mixture within the fuel tank.

FIG. 5 depicts an example routine 500 for a high-level method forrefueling a mixed liquid hydrocarbon/gaseous fuel system. In particular,routine 500 describes a method for liquid fuel refueling in a mixed fuelsystem. Routine 500 will be described herein with reference to thecomponents and systems depicted in FIGS. 1 and 3, though the method maybe applied to other systems without departing from the scope of thisdisclosure. Routine 500 may be carried out by controller 12, and may bestored as executable instructions in non-transitory memory.

Routine 500 may begin at 510 by determining whether liquid refueling isdesired. Determining whether liquid refueling is desired may includedirect and/or indirect liquid refueling requests from the vehicleoperator. Direct refueling requests may include explicit operatorrequests made through an interface or detection of an operator opening arefueling door. Indirect liquid refueling requests may include thedetection of a proximity to a refueling station. Proximity to arefueling station may be determined through GPS or other location data,or based on direct communication between the vehicle and refuelingstation. If no direct or indirect liquid refueling request is detected,method 500 may proceed to 515. At 515, method 500 may includemaintaining liquid refueling lock 367 closed. For example this mayinclude maintaining engagement of a refueling door with a latch via anelectromechanical actuator through a continued signal from a controller.Method 500 may then end.

If a direct or indirect liquid refueling request is detected at 510,method 500 may proceed to 520. At 520, method 500 may includedetermining whether pressure in the main fuel tank is less than a firstthreshold. Fuel tank pressure may be determined via fuel tank pressuresensor 211. If the fuel tank pressure is greater than the firstthreshold, method 500 may proceed to 515. At 515, method 500 may includemaintaining liquid refueling lock 367 closed. Method 500 may then end.

If the fuel tank pressure is less than the first threshold, asdetermined at 520, method 500 may proceed to 530. At 530, method 500 mayinclude determining whether the pressure in the main fuel tank is lessthan a second threshold, the second threshold being a lower pressurethreshold than the first threshold. The second threshold may be based onthe volume of secondary tank 390, and the amount of gaseous fuel thatmay be added to secondary tank 390. Fuel tank pressure may be determinedvia fuel tank pressure sensor 211. If the fuel tank pressure is lessthan the second threshold, method 500 may proceed to 540. At 540, method500 may include allowing liquid refueling. Allowing liquid refueling mayinclude opening liquid refueling lock 367. Allowing liquid refueling mayalso or alternatively include signaling to the vehicle operator orliquid fuel station attendant through an interface, indicating thatliquid refueling is allowed. Liquid refueling may continue until a fueltank pressure or fuel tank liquid level reaches a threshold, untilliquid fuel backs up to check valve 375, or until a liquid fueldispensing nozzle is disengaged from liquid refueling port 365. Method500 may then end.

If the fuel tank pressure is less than the first threshold and greaterthan the second threshold, as determined at 520 and 530, method 500 mayproceed to 535. At 535, method 500 may include pumping vapor from themain tank to the secondary tank. Pumping vapor from the main tank to thesecondary tank may include activating pump 385. Pumping vapor from themain tank to the secondary tank may continue until a pressure in fueltank 200 decreases below the second threshold, and/or until secondarytank 390 is filled. In some embodiments, pump 385 may be omitted fromrefueling system 350. In these embodiments, a valve may be opened toallow gaseous fuel and/or fuel vapor to proceed to secondary tank 390from fuel tank 200 via gaseous fuel line 380.

Following the pumping of vapor into secondary tank 390, method 500 mayproceed to 540. At 540, method 500 may include allowing liquidrefueling. Allowing liquid refueling may include opening liquidrefueling lock 367. Allowing liquid refueling may also or alternativelyinclude signaling to the vehicle operator or liquid fuel stationattendant through an interface, indicating that liquid refueling isallowed. Liquid refueling may continue until a fuel tank pressure orfuel tank liquid level reaches a threshold, until liquid fuel backs upto check valve 375, or until a liquid fuel dispensing nozzle isdisengaged from liquid refueling port 365. Method 500 may then end.

The systems described herein and depicted in FIGS. 1 and 3 and themethods described herein and depicted in FIG. 5 may enable one or moremethods. In one example, a method for refueling a vehicle fuel tank,comprising: responsive to a first condition, pumping gaseous fuel from afuel tank into a secondary vapor tank, while storing a hydrocarbonliquid fuel and a pressurized gaseous fuel only partially dissolved inthe hydrocarbon liquid fuel in the tank. The first condition may includethe detection of a liquid refueling request; and a fuel tank pressurethat is less than a first threshold, but greater than a secondthreshold, the second threshold less than the first threshold. Themethod may further comprise: responsive to a second condition, ceasingthe pumping of gaseous fuel from the fuel tank into the secondary vaportank; and enabling the addition of liquid fuel to the fuel tank. Thesecond condition may include a fuel tank pressure that is less than thesecond threshold. The technical result of implementing this method is arefueling strategy that allows for the addition of liquid fuel to a fueltank, even under conditions where the fuel tank pressure is above amaximally allowable threshold. In this way, liquid fuel may be added tothe tank when available for refueling, without requiring the combustionof additional gaseous fuel.

The systems described herein and depicted in FIGS. 1, 2, and 3 and themethods described herein and depicted in FIGS. 4 and 5 may enable one ormore systems. In one example, fuel tank system, comprising: a fuel tankconfigured to store a hydrocarbon liquid fuel and a pressurized gaseousfuel capable of partially dissolving in the hydrocarbon liquid fuel; arefueling conduit coupled to the fuel tank via a tank access valve; afirst high pressure refueling port coupled to the refueling conduit; alow pressure refueling port coupled to the refueling conduit via a checkvalve. The high pressure refueling port may be configured to receiveboth pressurized gaseous fuel and a pre-pressurized mixture of liquidfuel and gaseous fuel. The system may further comprise a second highpressure refueling port coupled to the refueling conduit, and further,the first high pressure refueling port may be configured to receivepressurized gaseous fuel, and the second high pressure refueling portmay be configured to receive a pre-pressurized mixture of liquid fueland gaseous fuel. The low pressure refueling port may be configured toreceive liquid fuel. The system may further comprise a surge tankcoupled between the low pressure refueling port and the check valve; aliquid level sensor coupled within the surge tank; and a refueling pumpcoupled between the surge tank and the check valve. The refueling pumpmay be configured to: during a first condition, pump liquid fuelcontained in the surge tank into the fuel tank. The first condition mayinclude: the detection of a liquid refueling request; a fuel tankpressure that is less than a first threshold; a fuel tank liquid levelthat is less than a second threshold; and a surge tank liquid level thatis greater than a third threshold. The system may further comprise asecondary vapor tank coupled to the fuel tank via a gaseous fuel line;and a depressurizing pump coupled to the gaseous fuel line between thesecondary vapor tank and the fuel tank. The depressurizing pump may beconfigured to: during a first condition, pump gaseous fuel from the fueltank into the secondary vapor tank. The first condition may include thedetection of a liquid refueling request; and a fuel tank pressure thatis less than a first threshold, but greater than a second threshold, thesecond threshold less than the first threshold. The system may furthercomprise a refueling lock coupled to the low pressure refueling port,the refueling lock configured to allow access to the low pressurerefueling port when the fuel tank pressure is below a threshold. Thetechnical result of implementing this system is a single fuel tankstoring both liquid fuel and pressurized gaseous fuel that may berefueled with liquid fuel, pressurized gaseous fuel, and/or apre-pressurized mix of liquid fuel and pressurized gaseous fuel. In thisway, a vehicle may obtain the benefits of having both liquid fuel andpressurized gaseous fuel available for combustion, without the need foradditional fuel tanks.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory. The specific routinesdescribed herein may represent one or more of any number of processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various actions, operations,and/or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedactions, operations and/or functions may be repeatedly performeddepending on the particular strategy being used. Further, the describedactions, operations and/or functions may graphically represent code tobe programmed into non-transitory memory of the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,1-4, 1-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A fuel tank system, comprising: a fuel tank configured to store aliquid fuel and a pressurized gaseous fuel capable of partiallydissolving in the liquid fuel; a refueling conduit coupled to the fueltank via a tank access valve; a first high pressure refueling portcoupled to the refueling conduit; a low pressure refueling port coupledto the refueling conduit via a check valve.
 2. The system of claim 1,wherein the first high pressure refueling port is configured to receiveboth pressurized gaseous fuel and a pre-pressurized mixture of liquidfuel and gaseous fuel.
 3. The system of claim 2, further comprising asecond high pressure refueling port coupled to the refueling conduit,and wherein: the first high pressure refueling port is configured toreceive pressurized gaseous fuel, and the second high pressure refuelingport is configured to receive a pre-pressurized mixture of liquid fueland gaseous fuel.
 4. The system of claim 1, wherein the low pressurerefueling port is configured to receive liquid fuel.
 5. The system ofclaim 4, further comprising: a surge tank coupled between the lowpressure refueling port and the check valve; a liquid level sensorcoupled within the surge tank; and a refueling pump coupled between thesurge tank and the check valve.
 6. The system of claim 5, wherein therefueling pump is configured to: responsive to a first condition, pumpliquid fuel contained in the surge tank into the fuel tank.
 7. Thesystem of claim 6, wherein the first condition includes: a detection ofa liquid refueling request; a fuel tank pressure that is less than afirst threshold; a fuel tank liquid level that is less than a secondthreshold; and a surge tank liquid level that is greater than a thirdthreshold.
 8. The system of claim 4, further comprising: a secondaryvapor tank coupled to the fuel tank via a gaseous fuel line; and adepressurizing pump coupled to the gaseous fuel line between thesecondary vapor tank and the fuel tank.
 9. The system of claim 8,wherein the depressurizing pump is configured to: responsive to a firstcondition, pump gaseous fuel from the fuel tank into the secondary vaportank.
 10. The system of claim 9, wherein the first condition includes: adetection of a liquid refueling request; and a fuel tank pressure thatis less than a first threshold, but greater than a second threshold, thesecond threshold less than the first threshold.
 11. The system of claim1, further comprising: a refueling lock coupled to the low pressurerefueling port, the refueling lock configured to allow access to the lowpressure refueling port when a fuel tank pressure is below a threshold.12. The system of claim 1, wherein the liquid fuel is gasoline, agasoline-alcohol blend, or diesel fuel, and the pressurized gaseous fuelis CNG. 13-16. (canceled)
 17. A method for refueling a vehicle fueltank, comprising: responsive to a first condition, pumping gaseous fuelfrom a fuel tank into a secondary vapor tank, while storing a liquidfuel and a pressurized gaseous fuel only partially dissolved in theliquid fuel in the fuel tank.
 18. The method of claim 17, where thefirst condition includes: a detection of a liquid refueling request; anda fuel tank pressure that is less than a first threshold, but greaterthan a second threshold, the second threshold less than the firstthreshold.
 19. The method of claim 18, further comprising: responsive toa second condition, ceasing pumping of gaseous fuel from the fuel tankinto the secondary vapor tank; and enabling addition of liquid fuel tothe fuel tank.
 20. The method of claim 19, where the second conditionincludes a fuel tank pressure that is less than the second threshold.